Crystallization

When crystallization is defined as the physical process of hardening, which results from the formation of crystals.

It can be made from a solution, melt, the gas phase, an amorphous solid or from a different crystal (recrystallization ), but always crystal formation and crystal growth. In this process, heat of crystallization is released. The emergence of the typical structure called " Kristalloblastese ".

Thus, a crystal can form the auszukristallisierende material must first be brought into supersaturation. This is done for example by cooling processes of solutions or melts, or by evaporation of the solvent. In crystals comprised of a plurality of components (for example, ionic crystals ), the supersaturation can also be prepared by mixing two solutions, each containing one of the components. It is also possible, by adding a third component to lower the solubility of already dissolved components and so as to create the supersaturation.

Here, the previously dissolved molecules or elements arranged in a regular, partly material-specific form. This process can be accelerated if seed crystals are added, which then grow in the supersaturated solution. The crystals can then be separated by filtration, flotation, centrifugation or sieving of the solution. An example of the extraction of a mass product by crystallization is the extraction of salt in salt pans.

Wherein the fractional crystallization is a mixture of substances is dissolved (for example, two or more isomers) in an appropriate solvent by heating. Is then prepared by cooling this solution or by slow evaporation of the solvent a supersaturated solution from which a substance crystallized preferred. Fractional crystallization is a process for the separation of substances. In some cases, even a resolution, so separation of the two enantiomers of a chiral substance, it is possible by fractional crystallisation. Another special case of fractional crystallization is the Rieselfilmkristallisation.